Technical Abstract:
Biological control of plant pathogens has enormous potential for solving intractable plant disease control problems, yet much of this potential remains unfulfilled. Our research addressed a serious impediment to bringing effective biological control products to the marketplace; the lack of adequate methodologies for mass producing biological control agents that have superior efficacy and amenability to the stresses of commercial-scale biomass production. Cryptococcus flavescens OH 182.9 reduces Fusarium head blight (FHB) severity on wheat by as much as 60% and deoxynivalenol in grain by nearly 30% in field experiments. The carbon loading and carbon-to-nitrogen ratio of fermentation media were optimized to enhance OH 182.9 product survival and efficacy. We further discovered that prolonged cold adaptation (28 hours) of colonized culture broth at 15 degrees centigrade enhanced the storage stability and efficacy of an OH 182.9 product. Cold adaptation improved liquid hyperosmotic shock tolerance and altered the temperature dependence of osmotic shock tolerance. Fluorescence anisotropy and force curves from atomic force microscopy suggested that cold adaptation significantly altered the membrane properties of OH 182.9. In other studies, the feasibility of obtaining the efficacy advantages of microbial mixtures by conducting bi- and tripartite, mixed-strain yeast fermentations was assessed. Growth curves of each component strain were determined by plating on a melezitose-based medium. A co-culture of OH 182.9 and C. aureus OH 71.4 that reached equivalent cell densities significantly reduced (32%) FHB disease severity in multiple greenhouse experiments. The possibility of obtaining superior efficacy and cost benefits with mixed-strain fermentation products justifies further evaluation of this approach.